The invention relates to a method for monitoring and controlling the regeneration of a particle filter in an exhaust gas duct of an internal combustion engine which has a three-way catalytic converter downstream of the particle filter in the direction of flow of the exhaust gas, wherein the particle filter is regenerated by oxidative burning of the particles during a regeneration phase, wherein oxygen consumption is balanced, directly or indirectly, during the regeneration phase via the temporal variation of a first signal of a first lambda probe, which is arranged upstream of the particle filter in the exhaust gas direction, in comparison to the temporal variation of a second signal of a second lambda probe, which is arranged downstream of the particle filter in the exhaust gas direction.
The invention furthermore relates to a device for carrying out the method according to the invention.
In order to reduce the particle emission from diesel engines and in future to an increasing extent from spark ignition engines (limit values according to EU6 from 2014), particle filters are inserted in the exhaust gas duct of the internal combustion engines. The exhaust gas is conducted through the particle filter which separates off the solid particles in the exhaust gas and retains said particles in a filter substrate. By means of the soot masses embedded in the filter substrate, the particle filter becomes clogged over time, this becoming apparent in an increase in the exhaust gas counterpressure with a negative effect on the engine performance and the fuel consumption. For this reason, the embedded soot mass has to be discharged from time to time. This filter regeneration takes place during special regeneration phases by oxidative burning of the particles, which runs automatically in the form of an exothermic reaction if there is an exhaust gas temperature of at least 580° C. and a sufficiently high concentration of oxygen in the exhaust gas. The course of the regeneration can be controlled via the composition of the exhaust gas and the exhaust gas temperature.
In addition to the particle filter, the exhaust gas aftertreatment of internal combustion engines requires further components. Thus, in the case of spark ignition engines which are operated according to a homogeneous concept, the pollutants hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) are converted via a three-way catalytic converter. In the case of lean concepts, a storage catalytic converter for nitrogen oxides is generally connected downstream. As little pollutant emission as possible is achieved by lambda control, with the fuel-air mixture supplied to the internal combustion engine being set on the basis of the concentration of oxygen in the exhaust gas. The oxygen fraction present in the exhaust gas is described by a lambda value which obtains the value 1 for stoichiometric combustion, the value>1 in the event of an excess of oxygen and a value<1 for a lack of oxygen. The lambda value is measured by corresponding lambda probes arranged in the exhaust gas duct.
The particle filter is generally regenerated if, as already explained above, a limit value for an exhaust gas counterpressure is exceeded. This can be detected by a suitable model and adjusted via a differential pressure measurement. In this case, the oxidation of the soot and therefore the regeneration of the filter are decisively influenced by the exhaust gas temperature and the residual oxygen content. Since an excess of oxygen has to be present in the exhaust gas in order to burn the particles, the mixture composition of the internal combustion engine cannot be freely selected in this phase as per the requirements of the driving mode. It is therefore desirable to determine an end of the regeneration in order to be able to switch to the normal driving mode.
The applicant's patent application which has not yet been published and has the official application number DE 10 2009 028237.8 discloses a method for monitoring and controlling the regeneration of a particle filter in an exhaust gas duct of an internal combustion engine, wherein the particle filter is regenerated by oxidative burning of the particles during a regeneration phase. In this case, it is provided that, during the regeneration phase of the particle filter, the internal combustion engine is operated at least temporarily at a lean operation point during lean operating phases or during oscillation of the mixture, and that the regeneration of the particle filter is monitored during the lean operating phases or during the oscillation of the mixture via the temporal variation of a second signal of a second lambda probe, which is arranged downstream of the particle filter in the exhaust gas direction, or of a second characteristic variable derived therefrom, in comparison to the temporal variation of a first signal of a first lambda probe, which is arranged upstream of the particle filter in the exhaust gas direction, or of a first characteristic variable derived therefrom. It is disadvantageous in this case that the regeneration takes place within a lean phase in which other harmful exhaust gas components cannot be optimally removed.
It is therefore the object of the invention to provide a method which permits reliable control and monitoring of the regeneration of the particle filter, wherein other harmful exhaust gas components can also be removed to an adequate extent from the exhaust gas.
It is furthermore the object of the invention to provide a corresponding device for carrying out the method.